Howdy Star Gazers and welcome to this episode
of Star Trails. Drew here and I'll be your guide
to the night sky for the week starting July the
6th through the 12th. This week we answer some
listener mail and explore the mystery of mass.
A big full moon looms low on the horizon, and
we take a detour into the icy reaches of our
solar system, where relics of the early universe
hide away in the darkness. Whether you're tuning
in from the backyard, the balcony, or just your
imagination, I'm glad you're here. So find a
cozy spot, let your eyes adjust, and let's see
what the sky holds for us this week. Before we
get into the night sky this week, I'd like to
kick off this episode with a listener question,
and this one really hits the sweet spot. Simple
on the surface, but it opens the door to something
surprisingly deep. Last week, Dale from Omaha
wrote, Can you explain mass? I don't understand
how mass is calculated or what that means. I've
heard astrophysicists say two planets are the
same size but have different masses. A simple
explanation would be greatly appreciated. Dale,
first off, thanks for writing in with this question,
and I know you asked for a simple explanation,
and I intend to provide one, but mass, although
a reasonably straightforward concept in and of
itself, is connected to some of the real mysteries
of astrophysics and the workings of the universe.
I'll get into a few of those in a moment, but
let's first figure out what's going on at the
most basic level. Mass is essentially how much
stuff is packed into something. It's not about
how big something looks, it's about how much
material is actually in there. Think about two
identical suitcases. One is filled with clothes,
The other is packed with bricks. They take up
the same space, but the one with bricks is a
lot heavier. That's because it has more mass.
Astronomers talk about mass all the time. Just
like your question, two planets can be the same
size, but one can have more mass. That means
one is denser. Maybe it has a larger metal core
or more rock and less gas. Same outside dimensions,
but more weight on the inside. Let's consider
Earth's planetary sister, Venus. Both Earth and
Venus are roughly the same size, but Earth has
more mass thanks to its larger metallic core.
Let's take another example. Because it's summer,
let's consider a beach ball compared to a bowling
ball, maybe a good 16 -pounder. The beach ball
is very light, but much larger than the bowling
ball. The beach ball contains mostly air, while
the bowling ball is filled with, well, whatever
bowling balls are made of, dense resin or plastics,
I assume. It's that density that matters, rather
than the size. And density is what determines
mass. Now, here's where things start to become
fascinating. Let's shrink ourselves down to the
molecular level. If you were to stand next to
a beach ball and a bowling ball at this tiny
size, you'd feel a gravitational pull towards
the bowling ball. Mass is directly tied to gravity.
The more mass something has, the stronger its
gravitational pull. Earth pulls harder than the
moon because it has more mass. The Sun keeps
the planets in orbit because it's massive, not
just in size, as the term is often used, but
in actual weight. In astronomy, we can't weigh
things directly, so we figure out mass by watching
how objects move. For example, how fast a moon
orbits a planet. That motion tells us how much
gravity there is, and gravity tells us the mass.
Now let's get weird. Mass accounts for some of
the most fascinating phenomena in the universe,
including one of the most extreme, black holes.
These are the ultimate examples of mass and gravity
gone wild. A black hole forms when a giant star
collapses and all that mass gets squeezed into
an incredibly tiny space. Imagine taking something
more massive than the sun and cramming it into
something the size of a city or smaller. The
result is unbelievably dense. Now remember, gravity
depends on mass, and our distance to an object
alters how much gravity we experience. Because
black holes are so compact, you can get extremely
close to them. But if you get too close, you
get sucked in, and there's no turning back. The
gravity near them is so strong that even light
can't escape. That's why they're black. If, purely
as a thought experiment, our sun turned into
a black hole, Earth would keep orbiting just
like it does now, same mass, same distance. But
if you flew close to that black hole, you'd cross
a point of no return, where gravity takes over
and there's no way back. We've understood the
relationship between mass and gravity for a while.
This was Isaac Newton's great breakthrough, later
expanded by Einstein and his theories of relativity
and space -time. Einstein also taught us that
energy and mass are basically interchangeable.
That, of course, is his famous equation E equals
mc squared. But interestingly, we don't really
know why mass affects gravity. This is one of
the real unsolved mysteries of the universe.
We just know that it does and that we can directly
observe its effect. There are some interesting
theories, gravitons for instance, particles that
somehow influence gravity. There are string theories
and theories based on that energy to mass relationship,
but so far we just don't really know. But we
do know what mass is and we know it shapes gravity.
motion, orbits, and the entire cosmic dance.
I know we went down a bit of a rabbit hole there,
but hopefully we answered the question. If anyone
out there listening has a question or a topic
they'd like for me to cover, just visit our website,
StarTrails .Show, and hit the contact link. Dale,
thanks so much for writing in. The night sky
is fairly quiet this week, and it will be dominated
by the upcoming full moon. On Thursday, we're
treated to the full buck moon rising in the evening
sky. The buck moon is the traditional name given
to July's full moon. It comes from, you guessed
it, Native American traditions, named after the
time of year when male deer began to grow their
new antlers. It's a moment that marks high summer,
and this year's buck moon has a little extra
drama. Because it's rising low on the horizon,
we'll experience what's known as the moon illusion.
That trick of the eye where the moon looks huge
when it's near the horizon, especially just after
it rises. Our brains compare it to nearby objects
like trees or rooftops, and we perceive it as
being much larger. It's a gorgeous effect, and
one of the best full moons of the year to photograph
if you have clear skies in your area. Now onto
the planets. Mercury is hanging out low in the
west -northwest just after sunset around magnitude
.3. Best seen early this week if you have a clear
view of the horizon. Mars is hanging out in the
west, still reddish but fading into the twilight.
Saturn and Neptune are up in Pisces, rising late
and sticking around into the night. Over in the
predawn sky, Venus is bright and unmistakable
in the east. Later in the week, it's joined by
a faint Uranus hiding in Taurus. As always, you'll
need a scope or good binoculars to spot Uranus
and Neptune. It's still early, but meteor season
is just around the corner. The Alpha Capra cornids
begin trickling in this week. Slow moving fireballs,
best later in July. And if you're a Perseid fan,
we're only about a week away from the start of
that shower's long lead up. Have you ever considered
how far our solar system extends from the sun?
In this episode, we're taking a little detour
beyond the outer planets into the frozen frontiers
of our solar system. We'll explore two of the
most mysterious regions we've never actually
seen with our own eyes, the Kuiper Belt and the
Oort Cloud. These are the deep freeze zones of
the cosmos, full of ancient icy leftovers, silent
travelers, and even the occasional supersized
comet. Let's start with the one closer to us.
The Kuiper Belt, named after the Dutch -American
astronomer Gerard Kuiper, is a ring of icy bodies
orbiting the sun beyond Neptune, starting around
30 astronomical units out. At that distance,
sunlight is a pale glow, and the temperature
is hundreds of degrees below zero. The Kuiper
Belt is the solar system's icy junkyard. It's
full of leftover material from when the planets
formed about 4 .6 billion years ago. We're talking
rocks, frozen gases, chunks of water ice, and
other elements that never made it into planets.
It's also home to some famous objects. Pluto,
of course, demoted from planet status in 2006,
is proudly orbiting in the Kuiper Belt. Eris
is slightly smaller than Pluto, but helped force
that whole redefinition of what a planet is.
Then there's Haumea, shaped like a football and
spinning so fast it completes a rotation every
four hours. And Machi Machi, another dwarf planet
named after a Polynesian creator god. These icy
worlds are known as Kuiper Belt Objects, or KBOs.
Many of them have moons, some have strange orbits,
and there are probably hundreds of thousands
more we haven't seen yet. NASA's New Horizons
mission flew past Pluto in 2015, revealing its
icy mountains, nitrogen glaciers, and unexpected
complexity. And then it kept going. sending back
images of another KBO, Arakoth, a reddish snowman
-shaped object about 21 miles long. That flyby
in 2019 gave us our very first close -up of a
true Kuiper Belt object. Now let's take a quick
detour about comets, snowballs in space with
glowing tails. Short period comets swing by the
Sun every few decades and often come from the
Kuiper Belt. Think of Comet Halley or Comet Temple
Tuttle. These objects orbit in more or less the
same plane as the planets, and their orbits are
usually predictable. But then there are the weird
ones, the comets with giant lopsided orbits that
take millions of years to return. That brings
us to our next destination. Far beyond the Kuiper
belt, somewhere between 2 ,000 and 100 ,000 astronomical
units from the Sun is a theoretical shell of
icy bodies called the Oort cloud. Unlike the
flat disc -shaped Kuiper belt, the Oort cloud
is spherical. Imagine a vast snow globe surrounding
our entire solar system, and inside that globe
are potentially trillions of icy fragments. comets,
planetesimals, ancient debris, left over from
the very formation of the Sun. We've never directly
seen the Oort cloud, it's just too far. But we
know it's there because of those long period
comets that suddenly appear from deep space on
incredibly eccentric orbits. Comets like Hale
-Bopp, which passed by in 1997 and won't return
for another 2500 years. Another such visitor
was comet C2012S1, which was hyped in 2013, but
broke apart near the Sun. And more recently,
there's a mega comet, and we mentioned this one
last week. In 2021, astronomers Pedro Bernardinelli
and Gary Bernstein spotted something strange
in data from the Dark Energy Survey. A fuzzy,
slow -moving object as wide as 85 miles across.
That's bigger than some small moons. Named comet
Bernardinelli -Bernstein, it's considered the
largest comet nucleus ever discovered. It's not
coming anywhere near Earth. At its closest approach
in 2031, it'll still be out past Saturn. Even
though we won't be able to see it with the naked
eye, this comet is giving scientists a rare opportunity
to study a pristine, early solar system object,
probably untouched since the sun was born. That's
like getting a piece of solar system history
frozen in deep space for billions of years. These
frozen regions are like the archives of the solar
system. The Kuiper Belt and the Oort Cloud preserve
the raw materials from the early days of planet
building, before Earth had oceans or life or
even before Jupiter finished forming. Some scientists
believe that comets from these outer zones delivered
water and organic molecules to the early Earth.
Others are looking into whether Oort Cloud comets
could help explain the odd tilt of Uranus or
even the idea of a hypothetical Planet Nine lurking
in the darkness. And that's our journey to the
far edge of the Sun's influence. From Pluto's
neighborhood to the Oort Cloud's distant reaches,
the outer solar system is more than just empty
space. It's a museum of frozen time. If the stars
spoke to you this week or if a question's been
on your mind, I'd love to hear it. Visit our
website, StarTrails .Show, where you can contact
me and explore past episodes. Be sure to follow
us on Blue Sky and YouTube. Links are in the
show notes. Until we meet again beneath the stars,
clear skies, everyone.